Ribbon-type magnetic armature transducer



June 9, 1959 R. M. CARRELL 2,890,239

RIBBON-TYPE MAGNETIC ARMATURE TRANSDUCER Filed June 1a, 1958 INVENTOR. EM CHEEELL IBM/w.

WMZZZZ United States Patent RIBBON-TYPE MAGNETIC ARMATURE TRANSDUCERRoss M. Carr-ell, Westmont, N.J., assiguor to the United States ofAmerica as represented by the Secretary or the Air Force This inventionrelates to a ribbon-type magnetic armature transducer which has a lowermechanical impedance than prior art devices and which, therefore, givesan increased efliciency.

One object of the invention is to provide a magnetic armature transducerwhich has less movable mass than prior art devices and which, therefore,has a better impedance match with the air.

This and other objects will be more fully understood from the followingdetailed description taken with the drawing wherein:

Fig. 1 is a top view of a magnetic armature transducer according to apreferred embodiment of the invention.

Fig. 2 is a sectional view of the device of Fig. 1 taken along the lines2-2.

In ordinary magnetic armature transducers, the ribbon armature must bemade stiff to offset the attraction of the pole pieces. Making thearmature stilt implies thickness which means added mass. According tothis invention, the stiffness is obtained by placing the armature undertension thereby permitting the use of much thinner material. Armaturethicknesses of .001 inch are possible, however, this would require veryaccurately balanced magnetic fields so that no D.C. flux flows throughthe armature to produce saturation and perfect balance is very difiicultto achieve in practice. Therefore, an armature thickness slightlygreater than .001 inch is required. In order to keep the total movingmass low, the armature is coupled to the diaphragm by a thin wire whichis kept under tension by a spring. The compliance of the spring shouldbe large compared with that of the diaphragm. The pole pieces areconstructed so that their reluctance is about percent of that of the airgap. Magnetic shunts are then provided to modify the reluctance of thepole pieces to adjust the fields so that the magnetic center of thestructure coincides with the armature.

Referring now to Fig. 1 of the drawings, reference character 10 refersto a magnetic armature transducer having a thin armature ribbon 11. Asshown in Fig. 2, armature ribbon 11 is supported on support posts 12 and13. The thickness of the armature should be approximately .001 inch.Magnetic pole pieces 14 and 17 are located on one side of the armatureand pole pieces 21) and 23 are located on the opposite side thereof.Pole piece 14 has projections 15 and 16 extending toward the armature.Pole piece 17 has projections 18 and 19 extending toward the armature.Pole piece 20 has projections 21 and 22 extending toward the armatureand pole piece 23 has projections 24 and 25 extending toward thearmature. A permanent magnet 26 is located between the pole pieces 14and 20 and a permanent magnet 27 is located between the pole pieces 17and 23. The output is taken off by means of coils 30 and 31 whichencircle the armature 11 and which are located between 7 the pole pieces14 and 20 and 17 and 23, respectively.

The coils 30 and 31 are connected in series aiding. A

diaphragm 32 is supported within a housing 33 in the usual manner and iscoupled to the armature 11 by means of a thin wire 34. The wire 34 iskept under tension by means of a spring 35 which is attached to thearmature 11 by means of a thin wire 36. The compliance of the spring 25should be made large compared with that of diaphragm 32. Magnetic shunts37 and 38 are provided adjacent the pole pieces 14 and 17 to adjust thereluctance of these pole pieces so as to make the magnetic center of thestructure coincide with the armature so that no D.C. flux will flowthrough the armature. As can be seen from Fig. 1, the magnetic shunts 37and 38 are located adjacent two holes 39 and 40 in the pole pieces.Though the hole is shown as being rectangular in shape in this figure,it is obvious that other configurations, as well as other locations forthe shunt elements, could be used.

There is thus provided a ribbon-type magnetic armature transducer whichhas less moving mass than prior art devices and which, therefore,provides an increased efiiciency.

While one specific embodiment has been described in some detail, it isobvious that numerous changes may be made without departing from thegeneral principles and scope of the invention.

What is claimed is:

1. A magnetic armature transducer, comprising; a thin ribbon-typearmature, means for supporting said armature under tension, a first polepiece located on one side of said armature, a second pole piece locatedon the other side of said armature, means for producing a magnetic fluxin said pole pieces, means adjacent said first pole piece for adjustingthe magnetic circuit through said pole pieces to thereby make themagnetic center of the structure coincide with said armature, adiaphragm, means for coupling said diaphragm to said armature and a coillocated in energy-coupling relation with said armature.

2. A magnetic armature transducer, comprising; a thin ribbon-typearmature, means for supporting said armature under tension, a first polepiece located on one side of said armature, a second pole piece locatedon the other side of said armature, means for producing a magnetic fluxin said pole pieces, means adjacent the pole piece on one side of saidarmature for adjusting the magnetic circuit through said pole pieces tothereby make the magnetic center of the structure coincide with saidarmature, a diaphragm, a thin wire for coupling said diaphragm to saidarmature, means connected to the other side of said armature for holdingsaid wire under tension and an output coil located in energycouplingrelation with said armature.

3. A magnetic armature transducer, comprising; a thin ribbon-typearmature, means for supporting said armature under tension, a first setof pole pieces located on one side of said armature, a second set ofpole pieces located on the other side of said armature, means forproducing a magnetic flux in said pole pieces, means adjacent the polepieces on one side of said armature for adjusting the magnetic circuitthrough said pole pieces to thereby make the magnetic center of thestructure coincide with said armature, a diaphragm, a thin wire forcoupling said diaphragm to said armature, means connected to the otherside of said armature for holding said wire under tension, and outputcoils located in energy-coupling relation with said armature.

4. A magnetic armature transducer, comprising; a thin ribbon-typeannature, means for supporting said arma- O ture under tension, a firstset of pole pieces located on producing a magnetic flux in said polepieces, a magnetic shunt adjacent the pole pieces on one side ofsaidarmature for adjusting the magnetic circuit through said pole piecesto thereby make the magnetic center of the structure coincide with saidarmature, a diaphragm, means having a low mass for coupling saiddiaphragm to said armature, means connected to the other side of saidarrnature for holding said coupling means under tension, and a pair ofoutput coils located in energy-coupling relation with said armature.

5. A magnetic armature transducer, comprising; a thin ribbon-typearmature having a thickness approximately .001 inch, means forsupporting said armature under tension, a first set of pole pieceslocated on one side of said armature, a second set of pole pieceslocated on the other side of said armature, means for producing amagnetic flux in said pole pieces, a magnetic shunt adjacent said firstset of pole pieces for adjusting the magnetic circuit through said polepieces to thereby make the magnetic center of the structure coincidewith said armature, a diaphragm, a thin Wire for coupling said diaphragmto said armature, means connected to the other side of said armature forholding said wire under tension and a pair of output coils located inenergy-coupling relation with said armature.

No references cited.

